Metal‐Free Arylation of Oxygen Nucleophiles with Diaryliodonium Salts

Phenols and carboxylic acids are efficiently arylated with diaryliodonium salts. The reaction conditions are mild, metal free, and avoid the use of halogenated solvents, additives, and excess reagents. The products are obtained in good‐to‐excellent yields after short reaction times. Steric hindrance is very well tolerated, both in the nucleophile and diaryliodonium salt. The scope includes ortho‐ and halo‐substituted products, which are difficult to obtain by metal‐catalyzed protocols. Many functional groups are tolerated, including carbonyl groups, heteroatoms, and alkenes. Unsymmetric salts can be chemoselectively utilized to obtain products with hitherto unreported levels of steric congestion. The arylation has been extended to sulfonic acids, which can be converted to sulfonate esters by two different approaches. With recent advances in efficient synthetic procedures for diaryliodonium salts the reagents are now inexpensive and readily available. The iodoarene byproduct formed from the iodonium reagent can be recovered quantitatively and used to regenerate the diaryliodonium salt, which improves the atom economy.     

Regiospecific syntheses of functionalized diaryliodonium tosylates via [hydroxy(tosyloxy)iodo]arenes generated in situ from (diacetoxyiodo)arenes

Ready access to (18)F-labeled aryl synthons is required for preparing novel radiotracers for molecular imaging with positron emission tomography. Diaryliodonium salts react with cyclotron-produced no-carrier-added [(18)F]fluoride ion to produce [(18)F]aryl fluorides. We aimed to prepare functionalized diaryliodonium salts to serve as potential precursors for producing useful (18)F-labeled aryl synthons, such as (18)F-labeled halomethylbenzenes, benzaldehydes, and benzoic acid esters. Such salts were designed to have one functionalized aryl ring, one relatively electron-rich ring, such as 4-methoxyphenyl or 2-thienyl, and a nonfluorine containing weakly nucleophilic anion. Generation of a [hydroxy(tosyloxy)iodo]arene from a functionalized (diacetoxyiodo)arene in situ followed by treatment with an electron-rich arene, such as anisole or thiophene, or with a functionalized arylstannane gave expedient regiospecific access to a wide range of functionally diverse diaryliodonium tosylates in moderate to high yields (44-98%). The described methodology broadens the scope for producing new functionalized diaryliodonium salts for diverse applications.     

Iron‐catalyzed carbon–sulfur bond formation: Atom‐economic construction of thioethers with diaryliodonium salts

Diaryliodonium salts are characterized by poor atom economy with the formation of one equivalent of an iodoarene as waste. We have developed an atom‐economic iron‐catalyzed protocol for the synthesis of a variety of thioethers with diaryliodonium salts. Not only cyclic diaryliodonium salts but also linear diaryliodonium salts were found to perform well in the reactions.     

Determination of Diaryliodonium Species by Reverse Iodometric Titration with Ascorbic Acid

Diaryliodonium salts are used in organic chemistry, materials science and pharmaceutical chemistry. For the quantitative analysis of diaryliodonium salts, only instrumentally demanding techniques requiring highly skilled operators are available. Surprisingly, no titration method taking advantage of the oxidising ability of diaryliodonium is available in the literature. In the present work, a titration method for the determination of diaryliodonium salts is presented. It is based on the reaction of diaryliodonium species with ascorbic acid, whose excess is subsequently determined by means of iodometric potentiometric titration. Application of the protocol to various diaryliodonium salts revealed the scope and limitations of the method.     

Synthetic application of water-soluble hypervalent iodine reagents in aqueous media

Along with the vigorous development of hypervalent iodine chemistry, water-soluble hypervalent iodine reagents have received considerable attentions in recent years. In order to obtain water-soluble hypervalent iodine reagents, two strategies have been employed including introduction of hydrophilic functional groups onto the phenyl ring and formation of complex of iodosylbenzene with crown ether. And, it is observed that four kinds of hypervalent iodine reagents exhibit more or less solubility in water including hypervalent iodine reagents containing hydrophilic ligands, diaryliodonium salts, oligomeric iodosylbenzene sulfate, and iodylbenzene and its derivatives. In this review, we summarize these water-soluble hypervalent iodine reagents and their broad synthetic applications in aqueous media.     

Copper-catalyzed direct N-arylation of N-arylsulfonamides using diaryliodonium salts in water

An efficient copper-catalyzed N-arylation of N-arylsulfonamides with diaryliodonium salts is reported. The reaction employs diaryliodonium salts and N-arylsulfonamides in water at room temperature, giving the products in moderate to excellent yields.     

Metal-free synthesis of aryl esters from carboxylic acids and diaryliodonium salts

An efficient arylation of carboxylic acids with diaryliodonium salts has been developed, giving aryl esters in high yields within short reaction times for both aromatic and aliphatic substrates. The transition-metal-free conditions are compatible with a range of functional groups, and good chemoselectivity is observed with unsymmetric diaryliodonium salts. Furthermore, steric hindrance in the ortho positions is well tolerated both in the carboxylic acid and in the diaryliodonium salt, yielding aryl esters that cannot be obtained via other esterification protocols.     

Concise synthesis of xanthones by the tandem etherification——Acylation of diaryliodonium salts with salicylates

An efficient synthetic method for multi-substituted xanthones was developed. The reaction of diaryliodonium salts and salicylates was employed for the preparation of the xanthones. This method proceeded through an intermolecular etherification-acylation to give target heterocycle in good yields (up to 91%). Multi-substituted xanthones were gained by shifting the substituent of salicylates or diaryliodonium salts.     

Direct arylation of tertiary amines via aryne intermediates using diaryliodonium salts

With a strategy by using diaryliodonium salts as the precursors of benzynes, direct N-arylation of tertiary amines with diaryliodonium salts was reported. Thus, the desired aromatic tertiary amines with a wide range of substituents were synthesized in moderate to excellent yields of 55–91%.     

The participation of the anion and alkyl substituent of diaryliodonium salts in photo‐initiated cationic polymerization reactions

The photo‐initiated cationic polymerization (PCP) of epoxides using diaryliodonium salt photoacid generators (PAGs) bearing alkyl groups and anions was investigated. The properties and reactivities of a series of iodonium salts containing various cations and anions were compared in the context of a PCP reaction. The products from the decomposition of the cations of these salts were analyzed using gas chromatography‐mass spectrometry (GC‐MS) spectra. The relationship between the molecular structure of the salts and their reaction mechanism in the PCP reaction was investigated. Based on the results of the investigation, it was concluded that the structures of the cations and anions of theiodonium salts affect the PCP reaction rate, which was controlled by the products from the diaryliodonium salts. As part of an additional investigation, the diaryliodonium salts‐epoxide materials were applied to 254 nm‐photo‐patterning. Copyright © 2006 John Wiley & Sons, Ltd.     

Domino N‐/C‐Arylation via In Situ Generation of a Directing Group: Atom‐Efficient Arylation Using Diaryliodonium Salts

Both aryl components of diaryliodonium salts can be used in a domino one‐pot reaction via in situ generation of a directing group. A number of heterocycles undergo N‐arylation which is followed by ruthenium‐catalyzed C‐arylation. Notably the reaction extends well to unsymmetrical diaryliodonium salts with a number of highly selective examples shown.     

Regiospecific one-pot synthesis of diaryliodonium tetrafluoroborates from arylboronic acids and aryl iodides

Diaryliodonium salts have recently received considerable attention as mild arylation reagents in organic synthesis. This paper describes a regiospecific, sequential one-pot synthesis of symmetrical and unsymmetrical diaryliodonium tetrafluoroborates, which are the most popular salts in metal-catalyzed arylations. The protocol is fast and high-yielding and has a large substrate scope. Furthermore, the corresponding diaryliodonium triflates can conveniently be obtained via an in situ anion exchange.     

Synthesis of Cyclic and Acyclic ortho-Aryloxy Diaryliodonium Salts for Chemoselective Functionalizations

Two regioselective, high-yielding one-pot routes to oxygen-bridged cyclic diaryliodonium salts and ortho-aryloxy-substituted acyclic diaryliodonium salts are presented. Starting from easily available ortho-iodo diaryl ethers, complete selectivity in formation of either the cyclic or acyclic product could be achieved by varying the reaction conditions. The complimentary reactivities of these novel ortho-oxygenated iodonium salts were demonstrated through a series of chemoselective arylations under metal-catalyzed and metal-free conditions, to deliver a range of novel, ortho-functionalized diaryl ether derivatives.     

C‐2 Selective Arylation of Indoles with Heterogeneous Nanopalladium and Diaryliodonium Salts

A simple and efficient method to prepare synthetically useful 2‐arylindoles is presented, using a heterogeneous Pd catalyst and diaryliodonium salts in water under mild conditions. A remarkably low leaching of metal catalyst was observed under the applied conditions. The developed protocol is highly C‐2 selective and tolerates structural variations both in the indole and in the diaryliodonium salt. Arylations of both N?H indoles and N‐protected indoles with ortho‐substituted, electron‐rich, electron‐deficient, or halogenated diaryliodonium salts were achieved to give the desired products in high to excellent isolated yields within 6 to 15 h at room temperature or 40 °C.     

Transition‐Metal‐Free N‐Arylation of Pyrazoles with Diaryliodonium Salts

A new synthetic method was developed for the N‐arylation of pyrazoles using diaryliodonium salts. The transformation does not require any transition‐metal catalyst and provides the desired N‐arylpyrazoles rapidly under mild reaction condition in the presence of aqueous ammonia solution as a mild base without the use of inert atmosphere. The chemoselectivity of unsymmetric diaryliodonium salts was also explored with large number of examples.     

Dye-sensitized photoinitiated cationic polymerization

Several dyes have been discovered which sensitize the photolysis of diaryliodonium salts at visible wavelengths. By using the combination of a dye and a diaryliodonium salt, visible light can be used to photoinitiate cationic polymerization. In this article, the dye-sensitized photopolymerizations of cyclohexene oxide, epichlorohydrin, and 2-chloroethyl vinyl ether are described.     

Synthesis and characterization of triarylsulfonium salts as novel cationic photoinitiators for UV-photopolymerization

Research on Chemical Intermediates - Using diaryliodonium salts as the arylating reagent and copper as a catalyst, a series of triarylsulfonium salts bearing benzoyl or benzoheterocyclic moieties...     

Radical-Promoted Visible Light Photoinitiated Cationic Polymerization of Epoxides

Herein is described the development of a three-component photoinitiator system that employs the free radical promoted decomposition of diaryliodonium salts for the visible light induced cationic polymerization of epoxides. A long wavelength, titanium-complex free radical photoinitiator is used to generate radicals that abstract hydrogen atoms from benzyl alcohol synergists. The resulting benzyl radical species efficiently reduce diaryliodonium salts thereby generating oxycarbenium ions that spontaneously fragment to form the corresponding aldehyde and a Br?nsted superacid. The superacid subsequently initiates the cationic ring-opening polymerization of a wide variety of epoxide monomers.     

Copper-catalyzed alkene arylation with diaryliodonium salts

Alkenes and arenes represent two classes of feedstock compounds whose union has fundamental importance to synthetic organic chemistry. We report a new approach to alkene arylation using diaryliodonium salts and Cu catalysis. Using a range of simple alkenes, we have shown that the product outcomes differ significantly from those commonly obtained by the Heck reaction. We have used these insights to develop a number of new tandem and cascade reactions that transform readily available alkenes into complex arylated products that may have broad applications in chemical synthesis.     

A Metal‐free Approach to 3‐Aryl‐3‐hydroxy‐2‐oxindoles by Treatment of 3‐Acyloxy‐2‐oxindoles with Diaryliodonium Salts

A mild, metal‐free approach has been realized for the facile construction of highly valuable 3‐(hetero)aryl‐3‐hydroxy‐2‐oxindoles. Direct arylations of 3‐acyloxy‐2‐oxindoles with diaryliodonium salts as arylation reagents are implemented in the presence of K₂CO₃ at room temperature without using an organometallic promoter to deliver an array of 3‐(hetero)aryl‐3‐hydroxy‐2‐oxindoles in good yields.